Energy storage system for increasing the flexibility of power plants

ABSTRACT

Provision of electricity to an electrical grid is controlled such that the electricity supply from the power plant is reduced to the current electric power demand by charging a thermal energy store(s). As a result, the provision of electricity by renewable energy sources to the electrical grid can be given precedence. The power plant can be connected to a heat pump and/or a refrigeration unit by the thermal energy store(s). The thermal energy store(s) can be used for district heating/cooling networks.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national stage of International ApplicationNo. PCT/EP2014/054122, filed Mar. 4, 2014 and claims the benefitthereof. The International Application claims the benefit of GermanApplication No. 102013209681.1 filed on May 24, 2013, both applicationsare incorporated by reference herein in their entirety.

BACKGROUND

Described below are energy conversion and storage systems for balancingfull-load and part-load periods of operation of power plants.

Although there is a great desire to replace conventional fossil-fuelpower plants, owing to the excessively high CO₂ emissions and theirimpact on the climate, and also nuclear power plants, owing to thevarious risks associated with them, by renewable sources of energy inorder to ensure a safer, more environmentally-friendly supply ofelectricity in future, ensuring an above all independent supply of powersolely on the basis of renewable sources of energy nevertheless stillremains a requirement. The conventional generation of electricity by,for example, fossil-fuel and nuclear power plants, at least in Germany,still represents over 50% of the power generated.

In order to expand renewable sources of energy such as, for example,biomass, photovoltaics or wind energy in addition to reliableindependent power generation, these very different forms of energygeneration need to be fed into the power grids in parallel. However,solar and wind power have the great disadvantage of being able to makeavailable only a highly fluctuating supply of power to the power grid.Up until now it has been possible for power to be stored only in verysmall quantities, as happens for example in batteries or pumped-storagepower plants or by flywheels. Depending on geographical conditions,potential energy stores such as, for example, pumped-storage powerplants are used, for example in Norway, but in most other countries theydo not offer an economically attractive solution, at least in the nearfuture, and in addition the storage quantity is limited.

In order to provide power flexibly to power grids, up until now forexample power plants with gas turbines or alternatively gas-and-steampower plants are known and are used because they can adjust their outputupward and downward relatively quickly. However, the number of suchpower plants is still very small. Moreover, the climate is furtherimpacted by burning natural gas and there is also a dependence on gasimported from other countries. Moreover, it is questionable to whatextent no-load and part-load periods of operation of these power plantsare still economical.

A different approach provides load management on the consumer side ofthe network which for this purpose needs to be a smart grid. Theexpansion of such smart grids so that they are comprehensive and reach asufficiently large number of users will, however, only solve part of theproblem and also reach its limitations.

Conventional power plants which are designed for a long-term foreseeablepower demand can be switched from full-load to part-load periods ofoperation only very slowly and only with high losses, or are switchedoff altogether. Depending on the power plant, this would take from atleast a few hours up to several days.

It is therefore a technical requirement to enable adjustable provisionof power by conventional power plants.

Solutions from the related art here relate to thermal storage solutionssuch as, for example, those known from DE 26 15 439 A1, DE 10 2008 050244 A1, FR 2 922608 A1, U.S. 2012/0047 891 A1 or U.S. 2013/0118170A1.

It is, however, a disadvantage of these solutions known from the relatedart that the thermal stores are not suitable or provided for efficientstorage of waste heat. In particular, the solutions known from therelated art disclose energy storage at a relatively high temperaturelevel, which can also result in relatively high heat loss and henceinefficiencies.

SUMMARY

In this respect, a technical storage solution is desired which not onlyallows thermal energy storage at a low temperature level but also makesit possible to make profitable use of waste heat of a power plant whichwould otherwise not be used further.

In addition to a power plant, at least one thermal energy store and atleast one energy conversion device are provided. The energy conversiondevice(s) is/are configured so as to charge the thermal energy storeduring a period of excess power supply, wherein a first heat store iscoupled to a condenser of the power plant. This has the advantage thatexcess power supply is not wasted and instead can be stored, and thissolution has the advantage that, in order not to generate any excesspower, the power plant does not need to be run unnecessarily expensivelyat part load or even switched off.

The coupling of the thermal store to a condenser of the power plantmakes it possible to discharge thermal energy, as a result of which thecooling demand in the condenser of the power plant is reduced. At thesame time, this coupling permits thermal storage, at a low temperaturelevel, of waste heat which would otherwise not be used further.

According to a further embodiment, it is provided that the thermal storeis coupled to the condenser of the power plant in such a way that it canbe charged with heat by the latter.

In an advantageous embodiment, an adjusting device for the provision ofpower to a power grid is also included. The adjusting device isconfigured so as to reduce the supply of power by the power plant bycharging the thermal energy store to the power demand that appliesduring this period so that the provision of power from renewable sourcesof energy to the power grid is prioritized. This has the advantage thateven individual inflexible conventional power plants can be used atfull-load operation for compensating adjustment behavior within a smartpower grid. The power plants can in particular be fossil-fuel powerplants which, in constant full-load operation, operate most efficientlywithout reducing the fuel mass flow, and at the same time the use andexpansion of renewable sources of energy can be increased.

The power plant is here in particular designed for constant full-loadoperation.

In a further advantageous embodiment, at least one thermal energy storeis a heat store, and at least one energy conversion device is a heatpump, wherein the heat store is discharged via a district heating grid.

In an alternative advantageous embodiment, at least one thermal energystore is a cold store, and at least one energy conversion device is arefrigerating machine configured to discharge the cold store via adistrict cooling grid.

This has the advantage that the heating or cooling demand within thevicinity of the site of the power plant can be met in anenergy-efficient fashion.

Furthermore, the first thermal store can be thermally coupled to anevaporator of a heat pump and/or to a condenser of a refrigeratingmachine. The thermal store can thus discharge heat to the evaporator ofthe heat pump or be charged additionally with heat by the condenser ofthe refrigerating machine. Especially when the evaporator of the heatpump is connected to the condenser of the power plant in such a way thatthermal energy is removed from there after the at least one turbine ofthe power plant, the total cooling demand of the power plant, especiallythe cooling demand in the condenser, is reduced very advantageously.

In a further advantageous embodiment, at least one energy conversiondevice is a heat pump and a second thermal store is thermally coupled toa condenser of the heat pump. In particular, it is coupled to thecondenser in such a way that it can be charged with heat by the latter.This second thermal energy store can particularly advantageously be usedto supply a district heating grid because a higher amount of thermalenergy can be stored as a result of the thermal coupling to thecondenser of the heat pump.

For example, at least one energy conversion device is a refrigeratingmachine, the evaporator of which is thermally coupled to a third thermalstore such that this third thermal store is charged with cold by theevaporator of the refrigerating machine and serves as a cold store. Thiscold store can be used particularly advantageously to provide cooling ina district cooling grid. As a result of the thermal store, the coolinggrid can be operated at staggered intervals.

Likewise, the district heating grid can be operated at staggeredintervals via the second thermal store. For example, it is also possibleto decouple a part heat flow from the power plant directly and hence tofeed the district heating grid, which corresponds to the previouscombined heat and power procedure, in order to compensate for any peakloads in the district heating grid when, owing to the requirements ofthe power grid and the power supply which is, for example, provided fromrenewable sources, the heat pump should not be put into operation. Theconnection of the condenser of the power plant to the evaporator of theheat pump is particularly energy-efficient because the waste heat of thepower plant for use in the district heating grid can be brought to amuch higher temperature level by the heat pump and simultaneously thecooling capacity of the power plant can be reduced. The use of water forcooling and the electrical fan capacity are thus reduced in the powerplant. It is, for example, also conceivable to use the waste heat ofcompressors, for example via water cooling circuits, to charge thesecond thermal store.

Water stores or phase change material stores are, for example, suitableas thermal stores.

In particular, the power plant can be connected to a district heatinggrid and simultaneously to a district cooling grid via a heat pump and arefrigerating machine, respectively, and both thermal grids can beoperated at staggered intervals via the respective thermal store. Inthis situation, a further connection can be made of the condenser of therefrigerating machine to the first thermal store which is connected tothe condenser of the power plant and the evaporator of the heat pump,and the waste heat of the refrigerating machine can thus be used atstaggered intervals for the evaporator of the heat pump. This is aparticularly advantageous energy-efficient synergy of the system ofmultiple components described herein.

It is particularly advantageous to couple a generator of the power plantand a compressor of at least one energy conversion device to the sameshaft.

Alternatively, the compressor or multiple compressors can also beoperated by indirect power transfer, for example via belts or withoutany direct power transfer at all, for example via the power grid. Theadvantageous embodiment of coupling compressors and the generator orturbine of the power plant on a common shaft reduces any power transferlosses. The coupling and decoupling of a rotating machine in ongoingoperation is known and does not contain any new technical requirements.

Both a refrigerating machine and a heat pump, or both of them at thesame time on the same shaft, can be operated like the generator of thepower plant. For example, in the combination with a refrigeratingmachine and with a heat pump too, in each case only one energyconversion device can be operated and it is thus possible to switch, forexample, from winter to summer operation.

All possible conventional power plants for power generation can beconsidered as a power plant in one of the described systems, for examplenuclear power plants, coal-fired power plants, biomass power plants,gas-fired or oil-fired power plants, etc. The respective power plantused can be operated at a constant fuel mass flow and neverthelessadjustable flexible electrical power can be provided using the heat pumpor the refrigerating machine. These power plants can thus also be usedwithin smart grids into which the feeding-in of renewable sources ofenergy can be prioritized.

In the method for the adjustable provision of power by a power plant, inwhich at least one thermal energy store which is thermally coupled to acondenser of the power plant and in particular is designed as describedabove and below is charged by an energy conversion device during aperiod of excess power supply, the power supply to a power grid by thepower plant is reduced by charging the at least one thermal store to thepower demand applied during the period, so that the provision of powerto the power grid from renewable sources of energy is prioritized. Inparticular, the power plant here runs at constant full-load operation.In an embodiment of the method, a heat store is used as a thermal energystore which is discharged via a district heating grid, in particularduring a period in which there is no excess power supply from the powerplant. Alternatively or additionally, a cold store is used as a thermalstore which is discharged via a district cooling grid, in turn inparticular during a period in which there is no excess power supply fromthe power plant. In the method, in particular at least one heat store ischarged by a heat pump and at least one cold store is charged by arefrigerating machine. This embodiment has the advantage of coveringthree different power demand periods. Multiple different power demandperiods can also be covered by multiple heat pumps or by multiplerefrigerating machines.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and advantages will become more apparent andmore readily appreciated from the following description of the exemplaryembodiments, taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 is a schematic block diagram of a power plant, thermal store,heat pump and refrigerating machine,

FIG. 2 is a schematic block diagram of a power plant combined with arefrigerating machine, and

FIG. 3 is a schematic block diagram of a power plant, thermal store,heat pump and refrigerating machine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the preferred embodiments,examples of which are illustrated in the accompanying drawings, whereinlike reference numerals refer to like elements throughout.

FIGS. 1 to 3 show in each case flow diagrams for a power plant processwith the charging and discharging of thermal energy stores T1 to T3,energy conversion processes 20, 40 which also exist, and energyconsumption grids 30, 50 connected to the stores T1 and T3. In eachcase, the power plant process 10 is shown on the left-hand side in thedrawing. The power plant in each case includes a generator 11 which isdriven by a turbine 12. Furthermore, the power plant includes acondenser 15, a feed pump 14, and a steam generator 13. All threedrawings show the most common type of power plant 10 with a steamcircuit. Power plants such as gas-and-steam power plants or a gas enginecan, however, also be coupled accordingly to a refrigerating machine 40or also to a heat pump 20. According to the example of a gas-and-steampower plant, its air compressor, gas turbine, and steam turbine could bearranged on a common shaft.

In FIG. 1, the power plant 10 is coupled to a heat pump 20. The latterhas a compressor 21, an evaporator 22, an expansion valve 23, and acondenser 25. Particularly advantageously, on the one hand a mechanicalpower connection needs to be produced between the power plant 10 and theheat pump 20 in such a way that the generator 11 and the turbine 12 ofthe power plant 10 and the compressor 21 of the heat pump 20 are coupledon a common shaft W. Furthermore, the power plant 10 and the heat pump20 are interconnected via the first thermal store T1, a heat store. Thelatter is charged by waste heat of the condenser 15, and the evaporator22 extracts the heat again from the thermal store T1. The condenser 25of the heat pump 20 is additionally connected to a second thermal storeT2, in turn a heat store, which is charged to a significantly highertemperature level as a result of the thermal coupling to the condenser25 of the heat pump 20. This is particularly suitable for beingdischarged via a district heating grid 30. The temperature level of thefirst thermal store T1 is, for example, between 50° C. and 90° C., andthe temperature level of the second thermal store T2 is, for example,between 80° C. and 130° C.

FIG. 2 shows an example for a steam power plant 10 with a refrigeratingmachine 40. The power plant 10 and the refrigerating machine 40 are hereagain connected via a common shaft W to which the generator 11 of thepower plant 10 and the steam turbine 12 are coupled, in exactly the sameway as the compressor 41 of the refrigerating machine 40. The uncouplingand coupling of the rotating machines takes place in ongoing operationin order to connect or disconnect the refrigerating machine 40 to thepower plant 10. The refrigerating machine 40 moreover includes anevaporator 42, an expansion valve 43, and a condenser 45. The evaporator42 is advantageously connected to a cold store T which is charged to atemperature level, for example between −20° C. and 15° C. and which candischarge its cooling via a district cooling grid 50. Waste heat againalso occurs at the condensers 15, 45 of the refrigerating machine 40 andof the power plant 10, at a temperature level between 30° C. and 90° C.,and can be charged for example to a further thermal store.

The charging of a thermal store T1 by the condenser 15 of the powerplant 10 and by the condenser 45 of the refrigerating machine 40 isshown in FIG. 3, in which the power plant 10 is coupled to a heat pump20 and a refrigerating machine. In this combination, a first heat storeT1 is charged with heat by the condensers 15, 45 of the power plant 10and of the refrigerating machine 40. This first heat store T1 may beused to operate the heat pump 20 by discharging its heat to theevaporator 22. The condenser 25 of the heat pump 20, which makes wasteheat available at a significantly higher temperature level, loads inparticular a second heat store T2 which is available to supply adistrict heating grid 30. The refrigerating machine 40 shown againsupplies a district cooling grid 50 which can be operated at staggeredintervals by the cold store T3. This combination is particularlyeffective in terms of energy efficiency when the rotating components 11,12, 21, 41 again are all operated on a common shaft W because anytransfer losses are thus avoided. It is shown in FIG. 3 that thegenerator 11 and the steam turbine 12, as well as the compressors 21 and41 of the heat pump and refrigerating machine, are arranged on a commonshaft W.

A description has been provided with particular reference to preferredembodiments thereof and examples, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the claims which may include the phrase “at least one of A, B and C”as an alternative expression that means one or more of A, B and C may beused, contrary to the holding in Superguide v. DIRECTV, 358 F3d 870, 69USPQ2d 1865 (Fed. Cir. 2004).

1-14. (canceled)
 15. A system, comprising: a power plant including acondenser; at least one thermal energy store, including a first thermalstore thermally coupled to the condenser of the power plant; and atleast one energy conversion device configured to load the at least onethermal energy store during a period of excess power supply.
 16. Thesystem as claimed in claim 15, further comprising an adjusting deviceadjusting provision of power to a power grid, configured to reduce thepower supply from the power plant by charging the thermal energy storeto the power demand that applies during a period of time and prioritizepower from renewable sources of energy to the power grid.
 17. The systemas claimed in claim 15, wherein the power plant operates mostefficiently under constant full-load operation.
 18. The system asclaimed in 15, wherein the at least one thermal energy store includes aheat store and the at least one energy conversion device includes a heatpump, and wherein the system discharges the heat store via a districtheating grid.
 19. The system as claimed in 15, wherein the at least onethermal energy store includes a cold store and the at least one energyconversion device includes a refrigerating machine, and wherein thesystem discharges the cold store via a district cooling grid.
 20. Thesystem as claimed in claim 15, wherein the at least one thermal energystore includes at least one of a heat store a cold store, wherein the atleast one energy conversion device includes at least one of a heat pumpwith an evaporator, and a refrigerating machine with a condenser, andwherein the first thermal store is thermally coupled to at least one ofthe evaporator of the heat pump and the condenser of the refrigeratingmachine.
 21. The system as claimed in claim 15, wherein the at least oneenergy conversion device is a heat pump having a condenser, and whereinthe at least one thermal energy store further includes a second thermalstore thermally coupled to the condenser of the heat pump.
 22. Thesystem as claimed in claim 15, wherein the at least one energyconversion device is a refrigerating machine with an evaporator, andwherein the at least one thermal energy store further includes a secondthermal store thermally coupled to the evaporator of the refrigeratingmachine.
 23. The system as claimed in claim 15, wherein the power plantincludes a generator having a shaft, and wherein the at least one energyconversion device includes a compressor coupled to the shaft of thegenerator.
 24. A method for adjustable provision of power by a powerplant, comprising: charging at least one thermal store thermally coupledto a condenser of the power plant by an energy conversion device duringa period of excess power supply; and reducing power supply to a powergrid by the power plant by said charging of the at least one thermalstore to a power demand applied during a first period of time, so thatprovision of power to the power grid from renewable sources of energy isprioritized.
 25. The method as claimed in claim 24, further comprisingrunning the power plant at constant full-load operation.
 26. The methodas claimed in claim 24, wherein the at least one a thermal energy storeis a heat store, and wherein said method further comprises dischargingthe heat store via a district heating grid during a second period oftime when no excess power is available from the power plant.
 27. Themethod as claimed in claim 24, wherein the at least one a thermal energystore is a cold store, and wherein said method further comprisesdischarging the cold store via a district cooling grid during a secondperiod of time when no excess power is available from the power plant.28. The method as claimed in claim 24, wherein the at least one athermal energy store includes at least one heat store and at least onecold store, and wherein said charging includes charging the at least oneheat store by a heat pump, and the at least one cold store by arefrigerating machine.